The transportation industry, including automobile and aircraft manufacturing, continues to expand the use of fiber reinforced polymer matrix composite parts to reduce weight, emissions and improve energy consumption and noise reduction. Common automobile composite parts are made by heat compression molding a preform sheet material made from glass fiber and thermoplastic resin. The aerospace industry requires materials with high strength modulus performance and typically uses unidirectional continuous fiber reinforced thermoset composite parts or carbon reinforcement impregnated with thermoset or high melt temperature advanced thermoplastic resins.
One common method of composite manufacture uses a pre-impregnated (prepreg) material made by applying a matrix resin onto a reinforcement fiber. The matrix resin may be a thermoplastic or thermoset resin applied onto a high tenacity reinforcement fiber. The fiber may be in a non-woven fabric of short or long fiber length or a woven or unidirectional fiber configuration of continuous fiber length. One method of prepreg manufacture is to apply a thermoplastic resin onto the reinforcement fiber or fabric by dip coating the fabric into a aqueous slurry made from micro-sized thermoplastic resin powder dispersed in water. The wet powder adheres to the fabric as the water is removed by drying. A consolidated prepreg can be made at this point by heating the prepreg under pressure and above the melt temperature of the resin. An alternative process is to heat the prepreg to partially melt the resin onto the fiber reinforcement to partially impregnate the prepreg. Complete impregnation of the prepreg is done during the composite part manufacturing and consolidation step.
Composite parts can be made by layup of the prepreg, where multiple layers are laid up by hand or mechanical means in a stacked configuration where subsequent layers are stacked having a defined fiber orientation. The laid up stack can than be processed by applying pressure and heat. Thermoset prepreg is normally processed in an autoclave under controlled pressure and heat to initiate a thermal chemical reaction to cure and consolidate the prepreg into a final composite part. Thermoplastic prepreg can be processed by layup in a mold and compression molded with pressure and heat to melt the thermoplastic resin throughout the fibrous stack. When the thermoplastic prepreg reaches the softening and melt temperature of the resin, the resin will flow into the fibers in a consolidation process and the prepreg will conform to fit the mold, producing the final composite part.
Several shortcomings in performance are inherent in manufacture of the prepreg by the aqueous slurry process. The polymer resin must be milled to a 25 to 50 micron particle diameter powder size, usually by cryogenic grinding, an expensive intermediate processing step. The polymer powder at 50 microns is much larger than the reinforcement fiber bundle diameter and therefore does not effectively penetrate into and uniformly wet the fibers during prepreg consolidation, producing a final composite with inadequate mechanical performance. The reinforcement fiber surface requires a surface treatment agent so that the polymer matrix resin will wet and tightly adhere to the fiber surface in order to produce a high quality prepreg. Typically, treating the fiber surface to wet the surface and improve adhesion of the polymer matrix resin to the fiber surface is called “sizing” the fiber.
The transportation manufacturing industry is looking for new composite materials and composite molding processes that deliver light weight, high strength-stiffness parts that address the issues of manufacturing cycle time, forming and joining, crashworthiness, safety, production cost and end of life recycle or reuse capability. The present invention is directed to a lower cost and faster manufacturing process for producing prepreg that overcomes the deficiencies of the prior art.